MariaMaria took the words out of my mouth - it is not recommended to run a marathon without having a year or two of consistant running under your belt. Most experienced runners will tell you that you should be running around 30 miles per week (mpw) for a few months before even begining marathon training. That's not to say that you can't complete a marathon at the end of 2011, but you're going to be much more prone to injury and it's going to be much harder. Running a half marathon at the end of the year is MUCH more obtinable goal - I went from couch to half marathon in about a year without any issues. It is only after 3 years of consistant running (I put in 500 miles in 2008, 830 miles in 2009 and 1,100 miles in 2010) that I am finally feeling ready to take on the marathon/ultramarathon distance. Which marathon did you sign up for?
If you don't want to go down to the half marathon (the race may let you switch even though you registered for the full marathon) and you're committed to training right for this marathon, then here we go...
You're running 3 miles per week right now? Is that a 3 mile run once a week or three 1 mile runs? You should look into Couch to 5K (C25K) and follow that plan so that you are comfortable running 3 miles 3-4 days a week (12mpw). Go run a 5K sometime in March or April to experience the race atmosphere.
You will need to slowly building your mileage up over the spring/summer. Don't increase your mileage by more than 10% each week. Take every 3rd week as a "cutback" week (reduce your mileage by 25%-ish) so your body gets some rest and you don't get burned out. Possibly follow a 10K or half marathon training plan during this time. Hal Higdon has some great free beginner programs (just google - it'll pop right up) that you could follow. Another poster recommended Jeff Galloway, which would be fine too.
Marathon training programs are typically 18 weeks long, which would put you starting yours around August. Running a half marathon during the middle of your marathon training will give you a good idea of where you are at.
Honestly, there's so much more to be said about this. I'm a regular poster over at the forums on Runner's World (but with a different user name) -- you could get some great advice over there. (Go to their forums section and then to Beginner's.) But if you do, be prepared to hear that you're not ready to tackle a marathon at the end of November. They're a great group over there, but they don't want to see anyone get injured either. But you'll get some great training advice if you stick around.
Sorry that was so long!
